Whereas most decorative wood facing is produced from hardwood, there are decorative wood types that are not truly hardwood. Reference herein to decorative hardwood is intended to encompass also decorative wood panels that are not truly hardwood.
Decorative wood panels, e.g., hardwood plywood panels, are used as decorative facings for cabinetry, furniture and the like. It is attractive in its natural hardwood shading. It has no repetitive pattern in the manner by which it is shaded and a part of its attractiveness is embodied in the unique shading of each hardwood facing.
Yet, defects are visually recognizable as distinguishable from the shading and are to be avoided. Whereas defective plywood facing is rejected prior to assembly of the facing sheets onto plywood, the assembly process itself can and does produce defects. These range from indentations to scratches to misaligned edges to thickness variations and so on.
Heretofore, such defects have been detected by visual inspection. However, the sheets are produced at a speed that makes visual inspection very difficult and it is estimated that 10% or higher of the defects are missed at the time of final inspection at the factory. The overlooked defective sheets are sent to customers who may well, at least partially, and/or occasionally produce an end product before the defect is discovered. Customers place high priority on obtaining defect-free decorative panels and it is accordingly highly desirable to detect defects following plywood assembly and before shipping them to a customer. Because visual detection is not satisfactory, it is desirable to develop an automatic system to detect such defects.
Scanning systems have been available for a number of years and are commonly used in the lumber producing industry and even in the subcategory of plywood production. A known system of defect detection has been developed, e.g., by the company Argos which is based on imagery or photography. Light is directed onto a subject from varying angles, and images are conveyed to a computer which detects shade differences that in turn identify defects. The system uses “detectors” and “classifiers” that first identify shade differences and then determines the extent of those differences. However, this system and all known prior systems have not been applied to the classification of production defects as may occur in the production of decorative e.g. hardwood plywood panels.